The answer
Flat rooflight maintenance is light: rinse the glass a few times a year, keep leaves and debris clear of the kerb and the roof outlet, and look at the seals and the covering around the unit after bad weather. A failed seal, shown by misting between the panes, means the sealed unit or the rooflight needs replacing.
Cleaning the glass
A flat rooflight sits close to level, so rain does less of the cleaning than it does on a window. Dust, pollen and leaf mould settle on the glass and leave a film in a dry spell. Wash the outside with clean water, a little mild washing-up liquid and a soft, long-handled brush or a water-fed pole from the ground or from a ladder at the roof edge. Rinse the glass well so no film is left to streak.
Inside, the glass is wiped like any window. A rooflight over a kitchen collects cooking grease on the room side, and a damp cloth with mild detergent clears it.
Do not climb onto the glass. Unless a unit is rated by its maker as a walk-on rooflight, it will not take foot traffic, and even a rated one needs the right grip underfoot. A flat roof is also easy to slip on when wet. If the roof is hard to reach safely, a window cleaner with the right equipment is the better choice.
Avoid abrasive pads, scrapers and strong solvents, which can scratch glass or damage the coating and the seals.
After building work nearby
Plaster dust, brick dust and paint spots from work on the house or next door cling to glass and are harder to shift than ordinary dirt. Rinse them off soon after, with a good flow of clean water, before they dry hard, and never scrape.
Clearing the kerb, the outlet and the roof around it
The glass is the part you see, and the roof around it carries most of the weather. Leaves, moss and silt gather against the upstand and at the roof outlet, and standing water at the foot of a kerb is a bigger risk to a flat roof than rain on the glass.
Look at the roof after the leaves fall in autumn and again after a hard storm. From a window, a ladder at the roof edge or the ground, check that the outlet is clear and that the water is draining away from the kerb. Clearing leaves from the roof is a job for someone who is safe working at height, and the roof should be reached by a ladder that is tied or footed, never by stepping across the glass.
Moss and algae
Moss that grows on the covering round the kerb holds moisture against the upstand. A soft brush clears it. Pressure washers can lift the surface of felt or force water under laps, so they do not belong on a flat roof covering.
Seals and the covering around the unit
Every rooflight has two sets of seals. The first is the perimeter, where the glazing meets the frame and the frame meets the kerb. The second is the junction between the kerb and the roof covering, where felt, EPDM or GRP is carried up the upstand and finished under a cover flashing.
An annual look is enough. Check that the sealant round the frame is intact and has not cracked or pulled away, that the cover strip at the top of the upstand still lies flat and that the covering has not lifted at the corners. Where a unit opens, the rubber gasket should sit evenly all round when the unit is shut, and the hinges and any motor should move freely.
On an electric model, run it open and closed once in a while so the mechanism does not stiffen. If it has a rain sensor, wipe the sensor lightly with a damp cloth.
The covering is part of the roof as a whole, so whoever looks after the roof looks after that edge too. If the covering is old, it is sensible to review it at the same time as the rooflight.
Wind-blown debris can lodge under a cover strip. Lift nothing yourself; if a strip has come loose, note where, because a loose strip is a sign the junction beneath wants looking at.
Signs that need attention
A flat rooflight that is kept clean can run for years without complaint. These are the signs that tell you to act:
- Misting between the panes: moisture trapped between the panes shows the perimeter seal of the sealed unit has given up, and cleaning cannot reach it. Fresh glazing or a fresh rooflight is the cure, and we supply and fit those.
- A stain or a drip on the reveal: water coming in at the junction needs investigating before the stain spreads. Note where and when it shows, because wind direction and heavy rain often point to the source.
- A cracked pane: a crack weakens the unit and can let water in, so the glass needs replacing.
- Condensation on the room-side glass: a damp film on the inner face in winter usually comes from humid air in the room. Better glazing and a frame with an insulating break keep the inner face warmer, which cuts it.
Fogging between the panes of a misted unit sits out of reach of any cloth, and its cause and cure are covered in misted and failed rooflight replacement.
When to call us
If a unit has misted, cracked or come to the end of its life, our free survey leads to a fixed quote that states which room, which unit and how big, and the new work comes under the 10-year workmanship guarantee. The money side of that job is covered in what drives the price of a flat roof skylight, and the overall picture for this kind of unit is on our flat roof rooflights page. You can reach us on 0113 436 0654.